This invention relates to the art of handheld fluid dispensers and, more particularly, to improvements in the pump drive unit of a battery operated, handheld fluid dispenser.
A battery operated, motorized fluid dispenser of the character to which the present invention is directed is shown, for example, in U.S. Pat. No. 5,716,007 to Nottingham, et al. which is assigned to the same assignee as the present invention and which is hereby incorporated herein by reference. In the latter dispenser, an electric motor is selectively connected to a battery source by a push button or trigger operated switch and, when energized, the motor operates a pump mechanism by which fluid in a supply container associated with the dispenser is pumped through a discharge opening.
While the battery operated dispenser in the Nottingham, et al. patent operates satisfactorily, component parts in the pumping mechanism are subjected to forces and frictional interengagement which causes undesirable wear of the parts, undesirable loading of the electric motor, and undesirably fast drainage of the batteries. More particularly in this respect, the pump driving arrangement includes an electric motor having an output shaft coaxial with the pump and carrying a cam which is cooperable with an aligned cam follower on the movable component of the pump such that rotation of the motor output shaft is translated into axial displacement of the follower and pump element in a cylinder portion of the pump. Each of the aligned cam and cam follower has a planar cam surface inclined at the same angle relative to the drive shaft and pump axes and coaxial therewith. The cam follower associated with the pump element is restrained against rotation relative to the motor shaft and pump axes, whereby the cam face on the cam component mounted on the motor shaft rotates relative to the cam face of the cam follower between full facial engagement therewith when the pump element is at one end of the stroke thereof and engagement of the radially outer edges of the axially outer ends of the cam and follower components when the pump element is at the other end of the stroke thereof. The interengaging relationship between the cam faces during relative rotation therebetween radially loads the drive motor shaft and the cam follower and pump element, and radially loads the interengaging portions of the cam faces during relative rotation therebetween. Such loading of the cam faces not only promotes wear therebetween but uneven wear. Moreover, radial loading of the cam follower urges the latter against the cylinder portion of the pump and, together with radial loading of the motor shaft, imposes loads on the motor which in turn causes undesirably high drainage of the batteries. All of these undesirable loading characteristics impose frictional interengagement between the parts which undesirably affects performance of the drive unit and pump element. Moreover, maintenance and/or part replacement resulting from wearing of the component parts and battery drainage is undesirably high.